Wafer positioning device with storage capability

ABSTRACT

The present invention provides a wafer positioning device having wafer storage capability. The wafer positioning device has a wafer platform with wafer lift pins, a wafer position sensor, and a storage location in close proximity to the wafer platform and the wafer position sensor. The storage location may be above the wafer position sensor, in which case the wafer position sensor retracts or rotates so that the wafer lift pins may elevate a positioned wafer past the position sensor to the storage location. Alternatively, the storage location may be between the wafer platform and the wafer positioning device. The storage location is preferably formed by a plurality of rotatable towers or a plurality of retractable lift pins that are operatively coupled to the wafer platform and that have wafer support portions capable of assuming both a wafer storage position and a wafer passage position.

This application is a division of U.S. patent application Ser. No. 08/960,906 filed Oct. 30, 1997 now U.S. Pat. No. 6,309,163.

BACKGROUND OF THE INVENTION

Proper centering of a semiconductor wafer is essential during wafer processing and transport in order to avoid costly errors such as nonuniform processing and/or wafer collision. During semiconductor device processing a wafer must be accurately centered on a wafer support platform in order to ensure the wafer will receive uniform processing across its entire face (e.g., uniformly deposited layers). Similarly, due to the rapid decrease in mechanical tolerencing associated with continually decreasing system footprint (i.e., the decrease of a fabrication system's lateral dimensions), a wafer must be accurately centered on the transfer mechanism in order to avoid collisions during semiconductor device transport, and in order to reduce the probability of the wafer sliding off or being dropped by the transfer mechanism. In addition some processes are sensitive to crystal orientation and require wafer alignment prior to being transferred to the processing chamber. Accordingly numerous wafer alignment and/or centering devices (i.e., positioning devices) exist.

Conventional centering devices typically comprise a rotatable platform having three or four wafer lift pins that lift a wafer off the platform and shift horizontally to center the wafer. A wafer position sensor positioned a small distance above the platform transmits information regarding the location of the wafer's center point to the wafer lift pins. In practice, because the wafer lift pins' horizontal movement is limited, the wafer lift pins may need to make multiple lift and shift operations to achieve the required movement of the wafer to achieve accurate centering. The wafer edge location is checked after each lift and shift operation to verify wafer centering was achieved, or to initiate additional wafer movement.

Like conventional centering devices, conventional wafer alignment devices typically comprise a platform having a rotatable surface and a wafer position sensor positioned a small distance above the platform. The wafer position sensor identifies when a flat/notched region of the wafer is in a predetermined position and transmits this information to the rotatable platform to cease rotation.

Because a wafer must be centered before it can be aligned, many conventional devices include both alignment and centering capabilities. However, whether for centering and/or alignment, wafer transfer to, wafer positioning at, and wafer transfer from conventional positioning devices (i.e., the wafer transfer and positioning operation) follows the same sequence: 1) a wafer handler extracts a first wafer from a multi-slot wafer carrier and transports the first wafer to the positioning device; 2) the positioning device positions the first wafer; and 3) the wafer handler returns the positioned first wafer to the multi-slot wafer carrier. Thereafter the sequence repeats and the wafer handler extracts a second wafer from the multi-slot wafer carrier and transports the second wafer to the positioning device, etc.

As indicated by the sequence described above, conventional wafer positioning devices allow only the wafer handler or the positioning device to operate at a given time (i.e., serial operation); the wafer handler remains idle while the positioning device operates, and the positioning device remains idle while the wafer handler operates. Such serial operation wastes equipment operating time, reducing throughput and increasing wafer costs. Accordingly a need exists for an improved wafer positioning device.

SUMMARY OF THE INVENTION

The present invention provides an improved wafer positioning device having a wafer storage location in addition to a wafer platform and a wafer position sensor. The wafer storage location enables simultaneous operation of the wafer handler and the positioning device (i.e., parallel operation), thereby allowing the inventive positioning device to achieve significant throughput increases.

In a first aspect one or more wafer storage locations exist above the wafer position sensor and the wafer position sensor is mounted so as to allow a wafer to travel therepast (e.g., rotatably or retractably mounted). In a second aspect additional or alternative wafer storage locations exist between the wafer platform and the wafer position sensor. A wafer presence sensor detects the presence of a wafer in the region between the wafer platform and the wafer position sensor and alters the operation of the wafer positioning device accordingly.

In a first embodiment the storage location is formed by three rotatable towers spaced evenly about the wafer platform at a position just beyond the circumference of the wafer to be positioned. Each tower has one or more wafer support portions positioned at desired elevations above the wafer platform. As the towers rotate the wafer support portions are selectively rotated inwardly for wafer storage or outwardly for wafer passage. Preferably towers comprising more than one wafer support portion are comprised of concentric tubes that allow independent rotation of each of the tower's wafer support portions. The wafer lift pins of the inventive positioning device can elevate a wafer to the elevation of each wafer support portion.

In operation, initially each wafer support portion is rotated outwardly (i.e., in the wafer passage position). The inventive positioner positions a first wafer, and the wafer lift pins elevate the positioned first wafer. Thereafter, the towers rotate to position the relevant wafer support portions under the wafer, creating a wafer storage location; while a wafer handler, operating in parallel with the inventive positioner, retrieves a second wafer from a wafer carrier, deposits the second wafer on the wafer platform and immediately picks up the first wafer from the storage location. The first wafer may then be returned to the wafer carrier or placed in a processing chamber. Thus the wafer storage location enables continuous parallel operation of the wafer handler and the wafer positioning device.

In a second embodiment of the invention the storage location is formed by wafer lift pins that elevate from the wafer platform to store a wafer above the platform. Like the rotatable towers of the first embodiment, the wafer lift pins of the second embodiment each have a wafer support portion capable of selectively assuming a wafer supporting position and a wafer passage position. In operation, initially each wafer support portion is rotated inwardly. The inventive positioner positions a first wafer, and the wafer lift pins elevate the positioned first wafer to a storage location. The wafer handler then removes the first wafer from the storage location formed by the wafer lift pins storage, the wafer support portions of the wafer lift pins assume the wafer passage position and the wafer lift pins lower into position beneath a second wafer positioned on the wafer platform.

The inventive wafer positioning device is twice as productive as conventional wafer positioning device as nearly a 100% productivity increase is realized prior to positioning of a third wafer. Other objects, features and advantages of the present invention will become more fully apparent from the following detailed description of the preferred embodiments, the appended claims and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A, 1B and 1C are diagrammatic side elevational views of a first aspect of the inventive wafer positioning device having rotatable towers; the wafer support portions of which may selectively assume a wafer passage position as shown in FIGS. 1A and 1B, or a wafer storage position as shown in FIG. 1C;

FIG. 2 is a top plan view of a fabrication system employing the inventive wafer positioning device;

FIG. 3 is a diagrammatic side elevational view of a second aspect of the inventive wafer positioning device of FIG. 1, wherein each rotatable tower has a plurality of wafer support portions;

FIGS. 4A and 4B are diagrammatic side elevational views of a third aspect of the inventive wafer positioning device having storage pins that elevate from the platform to store a positioned wafer;

FIG. 5 is a diagrammatic side elevational view of a fourth aspect of the inventive wafer positioning device having storage pins that elevate from the platform to center a wafer;

FIG. 6 is a side elevational view of a fifth aspect of the inventive wafer positioning device having an additional storage location above the position sensor and a wafer handler for transferring wafers thereto; and

FIG. 7 is a timing diagram useful in comparing the operation of the inventive wafer positioning device with the operation of a conventional wafer positioning device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1A, 1B and 1C are side elevational views of an alignment and/or centering type wafer positioner ila configured in accordance with a first aspect of the invention. The inventive wafer positioner 11 a comprises a wafer platform 13 that preferably is rotatable so as to facilitate wafer alignment and/or centering, retractable wafer lift pins 15 a, 15 b operatively coupled to the wafer platform 13 (i.e., coupled so as to lift a wafer from the wafer platform), a wafer position sensor 17 operatively coupled to the wafer platform 13 (i.e., coupled so as to sense the position of a wafer on the wafer platform 13) and positioned a small distance thereabove, and a plurality of rotatable storage towers 19 a, 19 b.

Each of the storage towers 19 a, 19 b has a wafer support portion 21 a, 21 b coupled thereto at a first elevation such that a first wafer storage location 23 (FIG. 1C) is selectively formed when the wafer support portions 21 a, 21 b are rotated (via rotation of the storage towers 19 a, 19 b) to the wafer supporting position (FIG. 1C) and such that a wafer may travel therepast when the wafer support portions 21 a, 21 b are rotated (via rotation of the storage towers 19 a, 19 b) to the wafer passage position (FIGS. 1A and 1B).

The wafer position sensor 17 is rotatably or retractably mounted so as to perform wafer sensing when in a first position (i.e., the wafer sensing position) and to allow a wafer to travel therepast when in a second position (i.e., the wafer passage position—shown in phantom).

The wafer lift pins 15 a, 15 b may be shiftably coupled (e.g., to the wafer platform 13, to the chamber floor, etc.) in order to provide wafer centering capability, and can extend to the first elevation. The wafer position sensor 17 is operatively coupled to a controller 25, which in turn is operatively coupled to the wafer platform 13, the wafer lift pins 15 a, 15 b, and the storage towers 19 a, 19 b for control thereof.

The operation of the inventive wafer positioner 11 a is described with reference to FIGS. 1A-C and 2. FIG. 2 shows a top plan view of a fabrication system 27 which contains the inventive wafer positioner referenced generally in FIG. 2 by the number “11”. As shown in FIG. 2 the fabrication system 27 contains a transfer chamber 29 which couples a first load lock 31 and a first processing chamber 33. The transfer chamber 29 contains a wafer handler 35 and the inventive wafer positioner 11. A wafer carrier 37 is shown within the load lock 31.

Regarding the operation of the inventive wafer positioner 11 a, initially the wafer lift pins 15 a, 15 b are in a retracted position at an elevation below the wafer supporting surface of the wafer platform 13, and the wafer support portions 21 a, 21 b and the wafer position sensor 17 (in phantom) are in the wafer passage position as shown in FIG. 1A. The wafer handler 35 extracts a first wafer 39 a from the wafer carrier 37 and places it on the wafer platform 13.

Assuming the inventive wafer positioner 11 is a centering and alignment type positioner, the wafer position sensor 17 assumes the wafer sensing position and the wafer platform 13 rotates the first wafer 39 a. The wafer position sensor 17 senses the center position of the first wafer 39 a and outputs the position information to the controller 25. The controller 25 sends a control signal to the wafer platform 13 to cease rotation, and to the wafer lift pins 15 a, 15 b to perform a number of lift and shift operations in order to center the first wafer 39 a. Thereafter the wafer platform 13 again rotates the first wafer 39 a, and the wafer position sensor 17 senses the wafer's center position to ensure the first wafer 39 a is accurately centered. Provided the first wafer 39 a is accurately centered, wafer alignment is performed. That is, the wafer platform 13 again rotates while the wafer position sensor 17 senses for the flat or notched region of the first wafer 39 a. Once the flat or notched region is sensed, the wafer position sensor 17 provides the wafer alignment information to the controller 25 which in turn signals the wafer platform 13 to cease rotation.

After the first wafer 39 a is positioned (e.g., centered and aligned), the wafer position sensor 17 assumes the wafer passage position (shown in phantom) and the wafer lift pins 15 a, 15 b elevate the first wafer 39 a to a position above the wafer supporting portions 21 a, 21 b (FIG. 1B). Thereafter the rotatable storage towers 19 a, 19 b rotate such that the wafer support portions 21 a, 21 b assume the wafer supporting position (forming the storage location 23 of FIG. 1C); and the wafer lift pins 15 a, 15 b retract to a position below the wafer supporting surface of the wafer platform 13 and a second wafer 39 b is placed on the wafer platform 13 (as shown in FIG. 1C).

While the first wafer 39 a is being centered, aligned and placed in the storage location 23, the wafer handler 35 travels back to the load lock 31, extracts the second wafer 39 b from the wafer carrier 37, and, after the wafer lift pins 15 a, 15 b have sufficiently retracted, places the second wafer 39 b on the wafer platform 13. Such parallel operation of the wafer handler 35 and the inventive wafer positioner 11 allows the wafer handler 35 to proceed to the storage location 23 to extract the first wafer 39 a therefrom directly after depositing the second wafer 39 b on the wafer platform 13 (i.e., the second wafer placement and the first wafer extraction occur consecutively).

Thereafter positioning of the second wafer 39 b takes place directly after positioning of the first wafer 39 a without waiting while the wafer handler operates (i.e., positioning of the first and second wafers occur consecutively). While the second wafer is being positioned the wafer support portions 21 a, 21 b assume the wafer passage position (FIG. 1A), and the process described above repeats until each wafer within the wafer carrier 37 has been processed.

FIG. 3 is a diagrammatic side elevational view of a second aspect of the invention, showing an inventive wafer positioner 11 b, having additional storage locations 40 a, 40 b. The additional storage locations 40 a, 40 b are formed by additional wafer support portions 21 a′, 21 b′ at a second elevation; and additional wafer support portions 21 a″, 21 b″ at a third elevation, respectively. Thus, the first storage tower 19 a comprises the wafer support portion 21 a and the two additional wafer support portions 21 a′ and 21 a″; and the second storage tower 19 b comprises the wafer support portion 21 b and the two additional wafer support portions 21 b′ and 21 b″. So that each wafer support portion may be rotated individually, the first storage tower 19 a comprises a plurality of concentric tubes 41 a-c, and the second storage tower 19 b comprises a plurality of concentric tubes 41 d-f. Preferably each concentric tube 41 a-f has only one wafer support portion coupled thereto as shown in FIG. 3.

Aside from the additional storage locations 40 a, 40 b, and the inventive wafer positioner 11 b of FIG. 3 is structurally identical to the inventive wafer positioner 11 a of FIG. 1. Similarly the wafer positioner 11 a and wafer positioner 11 b operate identically, with the exception that the wafer lift pins 15 a, 15 b of FIG. 3 extend to each storage location 23, 40 a, 40 b (i.e., to the first, second and third elevations). When the wafer lift pins 15 a, 15 b transport a wafer to one of the additional storage locations 40 a, 40 b the wafer position sensor 17 assumes the wafer passage position as shown in phantom in FIG. 3.

The additional storage locations 40 a, 40 b provide greater flexibility, for example, enabling the inventive wafer positioner lib to supply positioned wafers to more than one wafer handler. Thus the inventive wafer positioner 11 b of FIG. 3 enables fabrication systems having a number of differing configurations to optimize their wafer handler/positioner usage.

FIGS. 4A and 4B are side elevational views of an alignment type wafer positioner 11 c configured in accordance with a third aspect of the invention. FIGS. 4A and 4B show a pair of storage pins 43 a, 43 b each having a translation portion 45 a, 45 b translatably mounted to the wafer platform 13 for traveling between a storage level and a platform level, and having wafer support portions 47 a, 47 b mounted to the translation portions 45 a, 45 b, respectively. In order to provide wafer centering the storage pins 43 a, 43 b may be shiftably coupled to the wafer platform 13, like the wafer lift pins 15 a, 15 b of FIGS. 1A-C and FIG. 3.

The wafer support portions 47 a, 47 b may be retractably mounted on the translation portions 45 a, 45 b so as to provide a wafer supporting position when the wafer support portions 47 a, 47 b are extended (FIG. 4A), and a wafer passage position when the wafer support portions 47 a, 47 b are retracted (not shown). Alternatively the wafer support portions 47 a, 47 b of FIGS. 4A and 4B may be stationarily mounted to rotatable translation portions 45 a, 45 b (much like the storage towers 19 a, 19 b and the wafer support portions 21 a, 21 b of FIGS. 1A-C and 3) so as to provide a wafer supporting position when the wafer support portions 47 a, 47 b are rotated toward each other (FIG. 2A), and a wafer passage position when the wafer support portions 47 a, 47 b are rotated away from each other (not shown).

The wafer support portions 47 a, 47 b each have a sufficient surface area so that together they may provide stable wafer support. When the wafer supporting portions 47 a, 47 b are stationarily mounted to the translation portions 45 a, 45 b the platform 13 is configured with a first recess and a second recess (represented in FIG. 4B as “A” and “B”) in the wafer platform 13 adjacent the first and second translation portions 45 a, 45 b, respectively. The first and second recesses allow the wafer support portions 47 a, 47 b to rotate between the wafer supporting position and the wafer passage position while the translation portions 45 a, 45 b are in the platform level position.

When the translation portions 45 a, 45 b assume the storage level position and the wafer support portions 47 a, 47 b assume the wafer supporting position a wafer storage location 49 is formed (FIG. 4B). When the wafer storage location 49 is formed intermediate the wafer platform 13 and the wafer position sensor 17, a sufficient distance (referenced in FIG. 4B by the letter “C”) exits between the storage location 49 and the wafer position sensor 17 to allow wafer transfer to and from the storage location 49; a sufficient distance (referenced in FIG. 4B by the letter “D”) exists between the wafer platform 13 and the storage location 49 to allow wafer transfer to and from the wafer platform 13; and a sufficient distance (referenced in FIG. 4B by the letter “E”) exists between the translation portions 45 a, 45 b to allow a wafer (which may be off-center in any direction) to pass therebetween.

The wafer position sensor 17 may include a wafer presence sensor for detecting the presence of a wafer in storage location 49 or, alternatively a separate wafer presence sensor may be employed. The presence of a wafer in storage location 49 precludes the wafer position sensor 17 from determining if a wafer on the wafer platform 13 is centered. Accordingly, if a wafer is present in the storage location 49, preferably a controller 50 coupled to both the wafer position sensor 17 and to the wafer presence sensor delays wafer position sensing until the wafer has been removed from the storage location 49.

It should be noted that conventional wafer lift pins employed for centering a wafer do not require the wafer support portions 47 a, 47 b because conventional wafer lift pins are positioned closely enough such that the translation portions 45 a, 45 b lift the wafer. That is, conventional lifting and/or centering pins do not need to be spaced a sufficient distance “E” to enable a wafer to be transferred therebetween. Accordingly, conventionally the translation portions 45 a, 45 b lift the wafer and a separate wafer support portion 47 a, 47 b is not needed.

In operation, initially the translation portions 45 a, 45 b are in the platform level position and the wafer support portions 47 a, 47 b are in the wafer supporting position (FIG. 4A). The wafer handler 35 (FIG. 2) extracts a first wafer (not shown) from the multi-slot wafer carrier 37 and transports the first wafer to the wafer platform 13 of the inventive wafer positioner 11 c. The wafer platform 13 rotates while the wafer position sensor 17 determines whether the first wafer is centered. Thereafter, the storage pins 43 a, 43 b lift and shift the first wafer a number of times (followed by wafer rotation to determine wafer position) until the wafer position sensor 17 determines the first wafer is centered. Thereafter, to align the first wafer, the wafer platform 13 rotates until the wafer position sensor 17 detects a flat/notched region of the first wafer (indicating proper wafer alignment) and then signals the wafer support 13 to cease rotation.

After the first wafer is properly centered and aligned the translation portions 45 a, 45 b elevate lifting the first wafer from the wafer platform 13 to the storage location 49 (FIG. 4B) intermediate the wafer platform 13 and the wafer position sensor 17.

The inventive positioner 11 c and the wafer handler 35 operate in parallel. While the positioning device 11 c is positioning the first wafer the wafer handler 35 (FIG. 2) extracts a second wafer from the multi-slot wafer carrier 37 (FIG. 2) and while the wafer translation portions 45 a, 45 b elevate the first wafer to the storage position 49, the wafer handler 35 transports the second wafer to the wafer platform 13.

Because the distance “E” between the translation portions 45 a, 45 b of the storage pins 43 a, 43 b is sufficient to allow a wafer (which may be off center in any direction) to pass therebetween, the second wafer may be deposited on the wafer platform 13 despite the presence of the extended storage pins 43 a, 43 b. After the wafer handler 35 deposits the second wafer, it proceeds directly to the storage location 49 to extract the first wafer therefrom (i.e., the second wafer placement and the first wafer extraction occur consecutively).

Thereafter alignment of the second wafer takes place directly after alignment of the first wafer without waiting while the wafer handler 35 operates (i.e., alignment of the first and second wafer occur consecutively). To allow the second wafer to be positioned the wafer support portions 47 a, 47 b assume the wafer passage position (either by retraction or rotation as previously described) and the translation portions 45 a, 45 b lower to the platform level position (FIG. 4A). Once the translation portions 45 a, 45 b are in the platform level position (just beneath the second wafer) the wafer support portions 47 a, 47 b again assume the wafer supporting position; the spaces A and B in the wafer platform enable the wafer support portions 47 a, 47 b to rotate or extend from the wafer passage position to the wafer supporting position. The storage pins 43 a, 43 b are thus ready to elevate and store the second wafer as soon as alignment of the second wafer is complete. Although less preferred, the operating sequence can be reversed such that the wafer handler 35 deposits an incoming wafer in the storage location 49 and extracts a positioned wafer from the wafer platform 13.

FIG. 5 is a side elevational view of a centering type wafer positioner 11 d configured in accordance with a fourth aspect of the invention. In this aspect the wafer platform 13 acts as a buffer location for receiving incoming wafer's to be positioned while the storage pins 43 a, 43 b center the wafer. The inventive wafer positioner 11 d of FIG. 5 is identical to that of FIG. 4 except the wafer platform 13 need not rotate. In this embodiment two wafer position sensors 17 a, 17 b are preferably employed in order to accurately determine the position of the wafer, without rotating the wafer.

The operation of the centering type wafer positioner 11 d of FIG. 5 is similar to that of FIGS. 4A and 4B. Initially the translation portions 45 a, 45 b are in the platform level position and the wafer supporting portions 47 a, 47 b are in the wafer supporting position. A first wafer is placed on the wafer platform 13 and the translation portions and the wafer support portions mounted thereto elevate carrying the first wafer to the storage location 49 (between the wafer platform 13 and the wafer position sensors 17 a, 17 b). The storage pins 43 a, 43 b shift horizontally to center the first wafer based on information provided by the wafer position sensors 17 a, 17 b.

While the first wafer is being elevated and centered the wafer handler 35 (FIG. 2) extracts a second wafer from the multi-slot wafer carrier 37, transports the second wafer between the translation portions 45 a, 45 b, and places the second wafer on the wafer platform 13. After centering of the first wafer is complete, the wafer handler 35 extracts the centered first wafer from the storage location 49 and returns it to the multi-slot wafer carrier 37 while the wafer support portions 47 a, 47 b assume the wafer passage position and while the translation portions 45 a, 45 b assume the platform level position.

Once in position beneath the second wafer, the wafer support portions 47 a, 47 b again assume the wafer supporting position (via rotation or extension) and the translation portions 45 a, 45 b elevate, lifting the second wafer to the storage location 49 where centering occurs. In this manner, placement of the second wafer and extraction of the first wafer occur consecutively and centering of the first and second wafers occur consecutively.

FIG. 6 is a side elevational view of an inventive wafer positioner 11 e configured in accordance with a fifth aspect of the invention. The inventive wafer positioner lie comprises an auxiliary storage location 51, which may comprise one or more storage locations (e.g., conventional storage mechanisms; the inventive storage locations 23 and/or 40 a-b, as in FIG. 1C and FIG. 3; the inventive storage locations 49 as in FIGS. 4A-B and 5; etc.) above the wafer position sensor 17, and a transfer mechanism 53 operatively coupled to the wafer platform 13 and dedicated to transferring wafers between the auxiliary storage location 51 and either the wafer platform 13, or the storage location 49. The fifth aspect of the invention may be used in conjunction with any of aspects 1-4 of the invention in order to further enhance the versatility of the wafer transport and positioning process.

In operation a wafer is positioned in accordance with any aspect 1-4 of the invention and is then transferred either directly from the wafer platform 13 to the auxiliary storage location 51 via the transfer mechanism 53, or from the wafer platform 13 to the storage location 49 and then, via the transfer mechanism 53, to the auxiliary storage location 51. Thus, in the configuration of FIG. 6, the invention provides additional storage options that may be used in any sequence to further adjust for bottlenecks that may occur in a given transport and positioning operation.

FIG. 7 is a timing diagram useful in comparing the wafer transport and processing operation of the inventive wafer positioning device and the wafer transport and processing operation of a conventional wafer positioning device. FIG. 7 is representative of the operation of the inventive wafer positioning device when configured with only a first storage location, and without the additional or auxiliary storage locations 40 a-b, 51.

The conventional wafer transport and positioning operation is represented in the upper portion of FIG. 7. The wafer transport and positioning operation of the inventive positioning device, and of the wafer handler used therewith is represented in the lower portion of FIG. 7. To facilitate explanation the operating steps are abbreviated within FIG. 7 as follows:

Get N= extract wafer number N from the wafer carrier and transport wafer number N to the positioning device;

Put N= extract wafer number N from the positioning device and transport wafer number N to the wafer carrier;

Position N= position wafer number N.

At Time t₁

within the conventional system the wafer handler gets a first wafer from the wafer carrier and places it on the positioning device;

within the inventive system the wafer hander gets a first wafer from the wafer carrier and places it on the positioning device.

At Time t₂

within the conventional system the positioning device positions the first wafer while the wafer handler idles;

within the inventive system the positioning device positions the first wafer while the wafer handler travels to the wafer carrier.

At Time t ₃

within the conventional system the wafer handler continues to idle while the positioning device positions the first wafer;

within the inventive system the wafer handler gets a second wafer from the wafer carrier and transports it to the positioning device while the positioning device continues to position the first wafer. After the first wafer is positioned, the first wafer is transferred from the wafer platform to the storage location of the inventive positioning device. During the transfer of the first wafer from the wafer platform to the storage location, the wafer handler places the second wafer on the wafer platform of the inventive positioning device. Note that the time to lift each wafer to the storage location is negligible compared to the positioning time, and is therefore not shown in FIG. 7.

At Time t₄

within the conventional system the wafer handler transfers the first wafer from the positioning device to the wafer carrier while the positioning device idles;

within the inventive system the wafer handler transfers the first wafer from the storage location of the inventive positioning device to the wafer carrier while the positioning device positions the second wafer.

At Time t₅

within the conventional system the wafer handler gets a second wafer from the wafer carrier, while the positioning device idles;

within the inventive system the positioning device continues to position the second wafer.

At Time t₆

within the conventional system the wafer handler idles while the positioning device positions the second wafer;

within the inventive system the wafer handler gets a third wafer from the wafer carrier and transports the third wafer to the positioning device while the positioning device continues to position the second wafer. After the second wafer is positioned, the second wafer is transferred from the wafer platform to the storage location of the positioning device.

At Time t₇

within the conventional system the wafer handler idles while the positioning device continues to position the second wafer;

within the inventive system the wafer handler transfers the second wafer from the storage location of the inventive positioning device to the wafer carrier while the positioning device positions the third wafer and the wafer handler places the third wafer on the wafer platform of the inventive positioning device.

At time t₈

within the conventional system the wafer handler continues to idle while the positioning device positions the second wafer;

within the inventive system the wafer handler continues to position the third wafer.

At Time t₉

within the conventional system the wafer handler transfers the second wafer from the positioning device to the wafer carrier;

within the inventive system the wafer handler gets a fourth wafer from the wafer carrier and transports the fourth wafer to the positioning device while the positioning device continues to position the third wafer. After the third wafer is positioned, the third wafer is transferred from the wafer platform to the storage location of the inventive positioning device and the wafer handler places the fourth wafer on the wafer platform of the inventive positioning device.

Thereafter, as shown in FIG. 7, the sequence continues in the same manner. As FIG. 7 clearly depicts, the inventive wafer positioning device experiences significantly less idle time than the conventional wafer positioning device, thereby increasing throughput. In fact, the inventive wafer positioning device receives the fourth wafer while the conventional wafer positioning device is still removing the second wafer from the conventional positioning device (as shown at time t₉) Thus, the inventive wafer positioning device achieves nearly twice the throughput of conventional wafer positioning devices and provides a significant advantage over conventional wafer positioning devices.

The foregoing description discloses only the preferred embodiments of the invention, modifications of the above disclosed apparatus and method which fall within the scope of the invention will be readily apparent to those of ordinary skill in the art. For instance, although the storage mechanism shown in FIGS. 4 and 5 preferably extends upwardly from the wafer platform, it is not limited thereto. For example, the storage mechanism can be mounted above the wafer platform and can extend downwardly to extract the wafer from the wafer platform. Similarly, the “storage towers” may be replaced with wafer supporting portions that extend from the side walls of a surrounding chamber.

As well, the number of wafer lift pins, storage pins and/or storage towers may vary. For instance, a single lift pin, a single storage pin and/or a single storage tower with sufficient surface area to stabily support a wafer may be employed. However, in order to provide optimal wafer stability without excessive component costs, three wafer lift pins and three storage towers are preferred in the first and second aspects of the invention, and two storage pins are preferred in the third and fourth aspects of the invention. Additionally, the wafer positioning device of the present invention can be employed either for a rough preposition or for more sensitive positioning operations.

Accordingly, while the present invention has been disclosed in connection with the preferred embodiments thereof, it should be understood that other embodiments may fall within the spirit and scope of the invention, as defined by the following claims. 

The invention claimed is:
 1. A wafer positioning device comprising: a rotatable wafer platform; a mechanism coupled to the rotatable wafer platform and adapted to rotate the rotatable wafer platform; a plurality of wafer lift pins operatively coupled to the wafer platform; a pin lift mechanism coupled to the wafer lift pins and adapted to selectively lift the wafer lift pins; a wafer position sensor operatively coupled to the wafer platform and positioned adjacent the wafer platform and adapted to sense a position of a wafer on the wafer platform; and a storage mechanism configured to provide wafer storage above the rotatable wafer platform, wherein the storage mechanism is operatively coupled to the plurality of wafer lift pins so that a wafer may be transferred therebetween, and wherein the storage mechanism comprises a plurality of rotatable storage towers each having a wafer support portion wherein the rotatable storage towers are configured to selectively form a wafer storage location by selectively rotating between a wafer supporting position in which the wafer support portions extend horizontally inwardly toward the wafer platform and a wafer passage position in which the wafer support portions extend horizontally outwardly away from the wafer platform, the storage mechanism also comprising a mechanism coupled to the rotatable storage towers and adapted to rotate the rotatable storage towers.
 2. The apparatus of claim 1 wherein the pin lift mechanism also is adapted to selectively horizontally shift the wafer lift pins to provide the wafer lift pins with wafer centering capability.
 3. The apparatus of claim 1, wherein the wafer position sensor is capable of assuming a wafer sensing position and a wafer passage position.
 4. A wafer positioning device comprising: a wafer platform; a plurality of wafer lift pins operatively coupled to the wafer platform; a pin lift mechanism coupled to the wafer lift pins and adapted to selectively lift the wafer lift pins, the pin lift mechanism also being adapted to selectively horizontally shift the wafer lift pins to provide the wafer lift pins with wafer centering capability; a wafer position sensor operatively coupled to the wafer platform and positioned adjacent the wafer platform and adapted to sense a position of a wafer on the wafer platform; and a storage mechanism configured to provide wafer storage and to allow a wafer to be transferred to the storage mechanism by the plurality of wafer lift pins, the storage mechanism comprising: a plurality of rotatable storage towers each having a wafer support portion wherein the rotatable storage towers are configured to selectively form a wafer storage location by selectively rotating between a wafer supporting position in which the wafer support portions extend horizontally inwardly toward the wafer platform and a wafer passage position in which the wafer support portions extend horizontally outwardly away from the wafer platform, the storage mechanism also comprising a mechanism coupled to the rotatable storage towers and adapted to rotate the rotatable storage towers.
 5. The apparatus of claim 4, wherein the wafer position sensor is capable of assuming a wafer sensing position and a wafer passage position.
 6. A wafer positioning device comprising: a wafer platform; a plurality of wafer lift pins operatively coupled to the wafer platform; a pin lift mechanism coupled to the wafer lift pins and adapted to selectively lift the wafer lift pins, the pin lift mechanism also being adapted to selectively horizontally shift the wafer lift pins to provide the wafer lift pins with wafer centering capability; a wafer position sensor operatively coupled to the wafer platform and positioned adjacent the wafer platform and adapted to sense a position of a wafer on the wafer platform; and a storage mechanism configured to provide wafer storage and to allow a wafer to be transferred to the storage mechanism by the plurality of wafer lift pins, the storage mechanism comprising: a plurality of rotatable storage towers each having a wafer support portion wherein the rotatable storage towers are configured to selectively form a wafer storage location by selectively rotating about respective vertical axes between a wafer supporting position and a wafer passage position, the storage mechanism also comprising a mechanism coupled to the rotatable storage towers and adapted to rotate the rotatable storage towers.
 7. The apparatus of claim 6, wherein the wafer position sensor is capable of assuming a wafer sensing position and a wafer passage position.
 8. A wafer positioning device comprising: a wafer platform; a plurality of wafer lift pins operatively coupled to the wafer platform; a pin lift mechanism coupled to the wafer lift pins and adapted to selectively lift the wafer lift pins, the pin lift mechanism also being adapted to selectively horizontally shift the wafer lift pins to provide the wafer lift pins with wafer centering capability; a wafer position sensor operatively coupled to the wafer platform and positioned adjacent the wafer platform and adapted to sense a position of a wafer on the wafer platform; and a storage mechanism configured to provide wafer storage and to allow a wafer to be transferred to the storage mechanism by the plurality of wafer lift pins, the storage mechanism comprising a plurality of wafer support portions, each mounted for movement between a first position in which the wafer support portions collectively form a wafer storage location and a second position in which the wafer support portions do not obstruct travel of a wafer past the wafer storage location, the storage mechanism also comprising a mechanism coupled to the wafer support portions and adapted to move the wafer support portions between the first position and the second position; wherein the wafer support portions are not lifted while being moved from the second position to the first position.
 9. The apparatus of claim 8, wherein the wafer position sensor is capable of assuming a wafer sensing position and a wafer passage position. 